Apoptosis of airway epithelial cells induced by corticosteroids

AB - Meconium aspiration syndrome (MAS) is common among newborn children but its mechanism is unclear. The syndrome is known to produce a strong inflammatory reaction in the lungs resulting in massive cell death. In this work we studied lung cell death by apoptosis after meconium aspiration in forty two-week-old rabbit pups. Analyzing lung samples by ISEL-DNA end labeling demonstrated the specific spread of apoptotic bodies throughout the lungs. These bodies were shrunken and smaller in size compared to normal cells and many of them were lacking cell membranes. About 70% of all apoptotic bodies were found among the airway epithelium cell eight hours after meconium instillation. In comparison, among lung alveolar cells, only about 20% cells were apoptotic in the same animals. In meconium-treated lungs and A549 cells, a significant increase of angiotensinogen mRNA and Caspase-3 expression were observed. The pretreatment of cells with Caspase-3 inhibitor ZVAD-fmk significantly inhibited meconium-induced lung cell death by apoptosis. These findings demonstrate the apoptotic process in meconium-instilled lungs or A549 cells in culture. Our results show lung airway epithelial and A549 cell apoptosis after meconium instillation. We suggest that studies of lung airway epithelial cell death are essential to understanding the pathophysiology of MAS and may present a key point in future therapeutic applications.

The granules of neutrophils are rich in an array of different antimicrobial molecules that are released in a controlled manner to protect the host from invading pathogens. During chronic neutrophilic inflammation, an increasing number of activated neutrophils secrete granule contents into the extracellular space, where the focal excess of normally protective proteases in the absence of pathogens can become destructive [ 18 ]. Intracellularly, neutrophil serine proteases (NSPs) help to destroy ingested bacteria within the phagolysosome. The family of NSPs include neutrophil elastase (NE), proteinase 3 (PR3), and cathepsin G (CG), all located in the primary azurophilic granules, and are together capable of degrading most of the extracellular matrix components such as elastin and collagen [ 57 , 58 ]. The most studied of these proteases as a drug target is neutrophil elastase, the net activity of which is increased in patients with alpha-1-proteinase deficiency (A1ATD). The genetic loss of this gene results in early-onset emphysema [ 59 ]. The hypothesis that COPD is caused by a protease-antiprotease imbalance is further strengthened by studies with exogenous instillation of elastase (or other neutrophil serine proteases) into animal lungs that leads to emphysema [ 60 , 61 ]. NSPs are amongst the most potent known stimulants of mucus secretion from epithelial cells [ 62 , 63 ], hypersecretion of which is a common feature across the neutrophilic diseases including cystic fibrosis, bronchiectasis, and chronic bronchitic COPD. Neutrophil elastase may worsen mucus-driven airway obstruction via two processes: activation of the sodium channel ENaC on the apical surface of epithelial cells (via degradation of SPLUNC1, the endogenous inhibitor of ENaC [ 64 ]) and indirect degradation of the cystic fibrosis transmembrane conductance regulator (CFTR) [ 65 ]. This would lead to dehydration of the airway surface and further weaken the ability of the airways to effectively clear not only mucus but any pathogens present therein.

AB - Environmental and occupational exposures to respirable ultrafine fractions of particulate matter (PM) have been implicated in the initiation and exacerbation of lung diseases. However, the precise mechanisms underlying production of cell damage and death attributed to nanoparticles (NP) on human airway epithelium are not fully understood. This study examined the role of neurotrophic pathways in NP-induced airway toxicity. Size and agglomeration of TiO2 nanoparticles (TiO2-NP) and fine (TiO2-FP) particles were measured by dynamic light scattering. Expression and signaling of key neurotrophic factors and receptors were assessed by real-time polymerase chain reaction, flow cytometry, immunostaining, and Western blot in various respiratory epithelial cells after exposure to TiO2-NP or TiO2-FP. Particle-induced cell death was measured by flow cytometry after annexin V/propidium iodide staining. The role of neurotrophin-dependent apoptotic pathways was analyzed with specific blocking antibodies or siRNAs. Exposure of human epithelial cells to TiO2-NP enhanced interleukin (IL)-1α synthesis, as well as nerve growth factor (NGF) gene expression and protein levels, specifically the precursor form (proNGF). TiO2-NP exposure also increased expression of p75NRF receptor genes. These neurotropic factor and receptor responses were stimulated by IL-1α and abolished by its specific receptor antagonist (IL-1-ra). TiO2-NP also increased JNK phosphorylation and apoptosis, which was prevented by anti-p75NRF or NGFsiRNA. Data demonstrated that TiO2-NP exerted adverse effects in the respiratory tract by inducing unbalanced overexpression of immature neurotrophins, which led to apoptotic death of epithelial cells signaled through the death receptor p75NTR. This may result in airway inflammation and hyperreactivity after exposure to TiO2-NP.

BIVENT was associated with reduced markers of inflammation, apoptosis, fibrogenesis, and epithelial and endothelial cell damage in lung tissue in both ALI models when compared to PCV. The inspiratory effort during spontaneous breaths increased during BIVENT-50 in both ALI models. In ALI(p), alveolar collapse was higher in BIVENT-100 than PCV, but decreased during BIVENT-50, and diaphragmatic injury was lower during BIVENT-50 compared to PCV and BIVENT-100. In ALI(exp), alveolar collapse during BIVENT-100 and BIVENT-75 was comparable to PCV, while decreasing with BIVENT-50, and diaphragmatic injury increased during BIVENT-50.

Apoptosis of airway epithelial cells induced by corticosteroids

BIVENT was associated with reduced markers of inflammation, apoptosis, fibrogenesis, and epithelial and endothelial cell damage in lung tissue in both ALI models when compared to PCV. The inspiratory effort during spontaneous breaths increased during BIVENT-50 in both ALI models. In ALI(p), alveolar collapse was higher in BIVENT-100 than PCV, but decreased during BIVENT-50, and diaphragmatic injury was lower during BIVENT-50 compared to PCV and BIVENT-100. In ALI(exp), alveolar collapse during BIVENT-100 and BIVENT-75 was comparable to PCV, while decreasing with BIVENT-50, and diaphragmatic injury increased during BIVENT-50.